[1H]Spin-echo nuclear magnetic resonance in plant tissue. I. The effect of Mn(II) and water content in wheat leaves.

The effect of age-dependent Mn(II)-gradients, as observed by electron paramagnetic resonance (EPR), on the [1H]NMR spin-spin relaxation time (T2) was studied in wheat leaves. A non-exponential T2 spin-echo decay was always observed, revealing the presence of at least two different fractions of non- (or slowly) exchanging water in the leaves. No effect of the Mn(II)-concentration on T2 of the separate water fractions (covering approximately 90% of the total water content) has been found. From these observations we conclude that Mn(II) is present in bound form. The dependence of T2 on water content can be explained with a two-state model, demonstrating the occurrence of fast exchange within each of the two slowly exchanging water fractions.     

Complex interactions between components of individual prey specialization affect mechanisms of niche variation in a grasshopper-hunting wasp

1.?Individual foraging behaviour defines the use of resources by a given population and its variation in different ways such as, for example, unpredictable interactions between taxon-biased and size-biased selection. Here we investigated how the environmental availability of prey and individual specialization, for both prey taxa and prey size, shape niche variation across generations in the grasshopper-hunting digger wasp Stizus continuus. 2.?The population of S.?continuus expressed selective predation, females mainly hunting species encountered on large bushes; diet changed across generations, due more to size increase in potential prey than to changes in the orthopteran community. 3.?Individual females of both generations weakly overlapped the size and taxa of prey, and the niche width of the second generation increased for both prey size and taxa. 4.?The greater variance in prey size in the environment accounted for the enlarged prey size niche of the second generation, but the load-lifting constraints of the wasps maintained individual prey size specialization constant. In contrast, the enlarged prey taxon niche paralleled a smaller overlap of diets between wasps in the second generation. 5.?Increased niche width in the S.?continuus population was thus achieved in two ways. Regarding prey size, all individuals shifted towards the use of the full set of available resources (parallel release). For prey taxa, according to the classical niche variation hypothesis, individuals diverged to minimize resource use overlap and perhaps intraspecific competition. These two mechanisms were observed for the first time simultaneously in a single predator population.     

Intraguild interactions between two biological control agents in citrus fruit: implications for biological control of medfly

The parasitoid wasp Spalangia cameroni and the predatory beetle Pseudoophonus rufipes have long been studied for use as biological control agents against the Mediterranean fruit fly Ceratitis capitata, particularly in citrus fruit orchards. Nevertheless, these two species of natural enemies, when competing for a common resource, may experience intraguild predation (IGP) interactions. These possible interactions, affecting parasitism and predation, have been evaluated in the present work, under laboratory conditions, through potential changes in functional response. Regarding host/prey density, both natural enemies, when acting alone, showed a type II functional response. Nevertheless, due to IGP, S. cameroni, in the presence of P. rufipes, showed a higher fertility rate and a type III functional response. The parasitism behaviour of S. cameroni was affected by the presence of the predator, reducing the host handling time. Conversely, the parasitism rate of S. cameroni did not vary in the presence of P. rufipes but the degree of superparasitism decreased and led to an increased fertility rate and an increasingly female‐biased sex ratio. Meanwhile, the predatory efficiency of P. rufipes was not affected by the presence of S. cameroni but discrimination between parasitised and unparasitised pupae of C. capitata, with a preference for the latter, was reported for this predator species. Our results suggest that in biological control programmes, the use of only one of these species is recommended at low infestation levels, whilst at high densities of the pest, the combination of both natural enemies seems to be the most appropriate strategy.     

Thin liquid films and monolayers of DMPC mixed with PEG and phospholipid linked PEG

In this work thin liquid films (TLFs) and monolayers at the air/water interface formed by dimyristoylphosphatidylcholine (DMPC) and by DMPC mixed with poly ethylene glycols (PEGs) and dimyristoylphosphatidylethanolamine (DMPE) linked PEGs were studied. Film forming dispersions were composed of two types of particles: liposomes and micelles. TLFs stability, threshold concentration C _t (i.e., the minimum one for stable film formation), and hydrodynamic behavior were measured. At equivalent conditions, DMPC films were Newton black films (real bilayers), while DMPE-PEGs films were much thicker with free water between the monolayers. DMPE-PEG addition to DMPC films caused both C _t decrease (depending on PEG moiety length and Mw) and change of TLF formation mechanism. TLFs’ hydrodynamic behavior also strongly depended on DMPE-PEG content and Mw. It was observed that thinning of the DMPC and DMPE-PEGs films continued to different film types and thickness, being much thicker for the latter films. Addition of free PEGs (PEG-200/6000) did not alter TLF type or stability, but changed TLF thinning time, confirming that free PEGs with Mw<8000 could not penetrate in the membrane and alter “near-membrane” water layer viscosity. Monolayer studies showed improved formation kinetics of both adsorbed and spread films, decrease of surface tension (equilibrium and dynamic), and of film compression/decompression histeresis area in DMPE-PEGs monolayers compared with DMPC pure films. Our study shows that combining the models of phospholipid TLFs and monolayers provide the opportunity to investigate the properties of membrane surface and to clarify some mechanisms of its interactions with membrane-active agents.     

Efficient search for new resistant genotypes to the citrus tristeza closterovirus in the orange subfamily Aurantioideae

 Virulent isolates of the citrus tristeza virus (CTV) are continuously arising and their spread threatens the world citrus industry. Methods for effective utilization of material conserved in germplasm banks are needed in plant improvement. Two objectives are pursued in the present paper: a search for new CTV-resistant genotypes and tests of two strategies for this search. One of these tests is based on a study of genetic relationships among genera and species of the orange subfamily and the other on scores of molecular markers known to be linked to the CTV-resistant locus. Sampled plants were graft-inoculated with a mild CTV isolate (T-346) and two virulent ones (T-388 and T-305). Susceptible plants were those where CTV multiplication was detected beyond 4 months after inoculation. All cultivars of Poncirus trifoliata tested, as well as Severinia buxifolia and Atalantia ceylanica, were resistant to the three CTV isolates; Fortunella crassifolia (Meiwa kumquat) resists two of them. The finding of CTV resistance in this species, closely related to cultivated Citrus species, opens a new arena for CTV-resistance improvement of oranges and mandarines by sexual hybridization. The searching strategy based on phylogenetic data has been successful, whereas the other one may be worthwhile only when the search is restricted to the species where linkage analysis is available. A good documentation system that allows quick sampling of accessions to build up core collections and where the location of new and useful genes could be easily worked out, is suggested to enhance germplasm utilization. Received: 27 April 1997 / Accepted: 5 June 1997     

Increasing salt tolerance in the tomato

In this paper, a number of strategies to overcome the deleterious effects of salinity on plants will be reviewed; these strategies include using molecular markers and genetic transformation as tools to develop salinity-tolerant genotypes, and some cultural techniques. For more than 12 years, QTL analysis has been attempted in order to understand the genetics of salt tolerance and to deal with component traits in breeding programmes. Despite innovations like better marker systems and improved genetic mapping strategies, the success of marker-assisted selection has been very limited because, in part, of inadequate experimental design. Since salinity is variable in time and space, experimental design must allow the study of genotype x environment interaction. Genetic transformation could become a powerful tool in plant breeding, but the growing knowledge from plant physiology must be integrated with molecular breeding techniques. It has been shown that the expression of several transgenes promotes a higher level of salt tolerance in some species. Despite this promising result, the development of a salt-tolerant cultivar by way of transgenesis has still not been achieved. Future directions in order to overcome the present limitations are proposed. Three cultural techniques have proved useful in tomato to overcome, in part, the effects of salinity: treatment of seedlings with drought or NaCl ameliorates the adaptation of adult plants to salinity; mist applied to tomato plants grown in Mediterranean conditions improves vegetative growth and yield in saline conditions; and grafting tomato cultivars onto appropriate rootstocks could reduce the effects of salinity.     

Complex-to-Predict Generational Shift between Nested and Clustered Organization of Individual Prey Networks in Digger Wasps

Although diet has traditionally been considered to be a property of the species or populations as a whole, there is nowadays extensive knowledge that individual specialization is widespread among animal populations. Nevertheless, the factors determining the shape of interactions within food webs remain largely undiscovered, especially in predatory insects. We used an aggregation of the digger wasp Bembix merceti to 1) analyse patterns of individual prey use across three flying seasons in a network–based context; and 2) test the effect of four potential factors that might explain network topologies (wasp mass, nest spatial distribution, simultaneous nest-provisioning, prey availability). Inter-individual diet variation was found in all three years, under different predator-prey network topologies: Individuals arranged in dietary clusters and displayed a checkerboard pattern in 2009, but showed nestedness in 2008 and 2010. Network topologies were not fully explained by the tested factors. Larger females consumed a higher proportion of the total number of prey species captured by the population as a whole, in such a way that nested patterns may arise from mass-dependent prey spectrum width. Conversely, individuals with similar body mass didn’t form clusters. Nested patterns seemed to be associated with a greater availability of the main prey species (a proxy for reduced intra-specific competition). Thus, according with theory, clusters seemed to appear when competition increased. On the other hand, the nests of the individuals belonging to a given cluster were not more closely located, and neither did individuals within a cluster provision their nests simultaneously. Thus, a female-female copying behaviour during foraging was unlikely. In conclusion, wasp populations can maintain a considerable individual variation across years under different food web organizations. The tested factors only partially accounted for the shift in network properties, and new analyses should be carried out to elucidate how diet network topologies arise in wasp populations.     

A two-nucleotide deletion renders the mannose-binding lectin 2 (MBL2) gene nonfunctional in Danish Landrace and Duroc pigs

The mannose-binding lectins (MBLs) are central components of innate immunity, facilitating phagocytosis and inducing the lectin activation pathway of the complement system. Previously, it has been found that certain single-nucleotide polymorphisms (SNPs) in porcine MBL1 and MBL2 (pMBL1, pMBL2) affect mRNA expression, serum concentration, and susceptibility to disease, but the combinatory effect of pMBL1 and pMBL2 genotypes needs further elucidation. In the present study, pMBL1 and pMBL2 alleles, combined pMBL haplotypes, and MBL-A concentration in serum were analyzed in purebred Landrace (N?=?30) and Duroc (N?=?10) pigs. Furthermore, the combined pMBL haplotypes of 89 Piètrain × (Large White × Landrace) crossbred pigs were studied, and the genotypes of 67 crossbreds challenged with Escherichia coli were compared to their individual disease records. In the purebred animals, three non-synonymous SNPs and a two-nucleotide deletion were detected in the coding sequence of pMBL2. The two-nucleotide deletion was present at a frequency of 0.88 in the Landrace pigs and 0.90 in the Duroc pigs, respectively. In the crossbreds, the T allele of the SNP G949T in pMBL1—previously shown to have profound effect on MBL-A concentration even in the heterozygote condition—was detected in 47 % of the animals. Finally, an association was found between low-producing MBL genotypes and low body weight on the day of weaning in the same animals.     

Nuclear magnetic resonanceimaging of membrane permeability changes in plants during osmoticstress

The cell water balance of maize (Zea mays L., cv LG 11) andpearl millet (Pennisetum americanum L., cv MH 179) duringosmotic stress was studied non‐invasively using ¹H nuclearmagnetic resonance (NMR) microscopy. Single NMR parameter imagesof (i) the water content (ii) the transverse relaxation time (T₂)and (iii) the apparent diffusion coefficient (D_app)were used to follow the water status of the stem apical region duringosmotic stress. During stress there are hardly any changes in watercontent or T₂ of the stem region of maize. Incontrast, the apical tissue of pearl millet showed a ～ 30% decreaseof T₂ within 48 h of stress, whereasthe water content and D_app did not change. Thesechanges can be explained by an increase of the membrane permeabilityfor water. This conclusion is supported by results from scanningelectron microscopy, relaxation measurements of sugar solutionsand numerical simulations of the relaxation and (apparent) diffusionbehaviour of water in a plant cell.     

Host specificity of trichodinid ectoparasites of freshwater fish

Ciliophorons of the family Trichodinidoe comprise seven genera, all of which are commensolists or parasites - mainly on aquatic hosts such as other ciliophorans, coelenterates, planctonic crustaceans, molluscs, echinoderms, amphibians and fish. Although the first species of this family, Trichodina pediculus, was described from material collected from Hydra, most literature concerns the trichodinids of fish-particularly cultured freshwater fish. These ciliophorans have been implicated in severe disease and mortalities of fish, causing severe economic losses in various parts o f the world. In spite o f the confused taxonomy o f the Trichodinidae, it now appears that they fall into four distinct groups representing a line of specialization towards a more exclusive niche on the host fish. The more opportunistic species, with a broad host range, tend to be larger skin parasites, while the more specialized are smaller and usually only parasitize the gills o f their specific host.